Sensors Overview

Many system applications require the measurement of a physical or electrical condition, or the presence or absence of a known physical, electrical or chemical quantity. Analog sensors are typically used to monitor the environmental condition by generating a change in an electrical property as a result of a change in the environmental condition.

Typical phenomena that are measured:

  • Electrical signals and properties
  • Magnetic signasl and properties
  • Temperature
  • Humidity
  • Force, weight, torque and pressure
  • Motion and vibration
  • Flow
  • Fluid level and volume
  • Light and infrared
  • Chemistry

Typical sensor applications involve the monitoring of sensor parameters and controlling of actuators. The sensor signal chain, as shown below, consists of analog and digital domains. Typical sensors output very low amplitude analog signals. These weak analog signals are amplified and filtered, and converted to digital values using op amps, analog-to-digital or voltage-to-frequency converters, and are processed at the PIC® MCU. The analog sensor output typically needs proper signal conditioning before it gets converted to a digital signal.

signal-chain-control-loop.PNG

There are sensors that respond to these phenomena by producing the following electrical properties:

  • Voltage
  • Current
  • Resistance
  • Capacitance
  • Charge

These electrical properties are then conditioned by analog circuits before being driven to digital circuits. In this way, the environmental condition can be quantified and the system can make decisions based on the results.

The MCU controls the actuators and maintains the operation of the sensor signal conditioning circuits based on the condition of the signal detection. In the digital to analog feedback path, digital-to-analog converter (DAC), digital potentiometer and Pulse-Width-Modulator (PWM) devices are most commonly used. A MOSFET driver is commonly used for the interface between the feedback circuit and actuators such as motors and valves. Microchip offers a large portfolio of devices for signal chain applications.

The table below provides an overview of typical phenomena, the type of sensor commonly used to measure the phenomena and electrical output of the sensor.

Summary Of Common Physical Conditions and Related Sensor Types:

Phenomena Sensor Electrical Output
Magnetic Hall Effect
Magneto-Resistive
Voltage
Resistance
Temperature Thermocouple
RTD
Thermistor
IC
Infrared
Voltage
Resistance
Resistance
Voltage
Humidity Capacitive
Infrared
Capacitance
Current
Force, Weight, Torque, Pressure Strain Gauge
Load Cell
Piezoelectric
Mechanical Transducer
Resistance/Voltage
Resistance
Voltage or Charge
Resistance, Voltage, Capacitance
Motion and Vibration LVDT
Piezoelectric
Microphone
Ultrosonic
Accelerometer
AC Voltage
Voltage or Charge
Voltage
Voltage, Resistive, Current
Voltage
Flow Magnetic Flowmeter
Mass Flowmeter
Ultrasound/Doppler
Hot-wire Anemometer
Mechanical Transducer (turbine)
Voltage
Resistance/Voltage
Frequency
Resistance
Voltage
Fluid Level and Volume Ultrasound
Mechanical Transducer
Capacitor
Switch
Thermal
Time Delay
Resistance/Voltage
Capacitance
On/Off
Voltage
Touch Capacitance
Inductance
Resistance
Voltage
Current
Frequency
Proximity Capacitance
Inductance
Resistance
Voltage, Frequency
Current, Frequency
Voltage, Current
Light Photodiode Current
Chemical pH Electrode
Solution Conductivity
CO Sensor
Photodiode (turbidity, colorimeter)
Ion Sensor
Voltage
Resistance/Current
Voltage or Charge
Current
Current

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